Introduction
Cocaine remains a major contributor to drug-related emergency department visits and is associated with substantial cardiovascular morbidity and mortality. Cardiac complications range from transient conduction abnormalities to myocardial ischemia, cardiomyopathy, malignant arrhythmias, and sudden cardiac death (2,3).While enhanced sympathetic activity and coronary vasoconstriction are well-recognised contributors, cocaine also exerts direct toxic effects on cardiac ion channels (1-3).
Cocaine cardiotoxicity is caused by use-dependent blockade of cardiac sodium channels (Nav1.5), leading to QRS widening, rate-dependent conduction slowing, and arrhythmias. Sodium bicarbonate can reverse this and is potentially lifesaving..
Experimental and clinical evidence shows that cocaine inhibits fast sodium channels (Nav1.5) and modulates calcium and potassium currents (1-3). Sodium channel inhibition reduces the slope of phase 0 depolarisation, resulting in slowed ventricular conduction and QRS prolongation. This interaction is state- and use-dependent, intensifying at higher heart rates and with repetitive depolarisation, thereby explaining the association between tachycardia and progressive QRS widening (1-3).
Recognition of toxic sodium channel blockade is clinically important because management differs from that for ischemic or structural causes of wide-complex arrhythmias. In this context, sodium bicarbonate represents a targeted and potentially lifesaving intervention (2,4).
Case presentation
A 25-year-old man with no known chronic illnesses and no regular medications was brought to the emergency department for an altered mental status. On arrival, he was febrile, tachycardic, tachypneic, hypotensive, and actively seizing with associated myoclonus. Urine toxicology screening was positive for cocaine and amphetamines.
During early resuscitation, the patient developed worsening tachycardia with progressive QRS widening, which rapidly degenerated into cardiac arrest. Advanced life support was initiated, including endotracheal intubation and mechanical ventilation. Benzodiazepines were administered for seizure control. A bolus of hypertonic sodium bicarbonate was given, after which narrowing of the QRS complex was observed, followed by return of spontaneous circulation after approximately eight minutes.
Laboratory evaluation revealed severe lactic acidosis, markedly elevated creatine kinase consistent with rhabdomyolysis, and transient renal and hepatic dysfunction. Computed tomography of the head showed no acute intracranial pathology. The patient was admitted to the intensive care unit, where metabolic abnormalities were corrected, and organ function improved. He was discharged from the ICU in stable condition after six days and referred for psychiatric follow-up.
Initial electrocardiograms showed markedly prolonged QRS complexes with lateral ST-segment depressions and ST elevation in lead aVR. Following sodium bicarbonate administration, serial ECGs showed progressive QRS narrowing and stabilisation of cardiac rhythm, consistent with reversal of sodium channel blockade.
Discussion
Cocaine produces conduction abnormalities through direct inhibition of Nav1.5 channels, binding preferentially to activated and inactivated channel states (1). This interaction reduces inward sodium current and delays ventricular depolarisation. Because binding is use-dependent, tachycardia exacerbates conduction slowing and promotes QRS prolongation (1-3).
In addition to sodium channel inhibition, cocaine disrupts repolarising potassium currents, alters intracellular calcium handling, induces mitochondrial dysfunction, and triggers catecholamine excess and myocardial ischemia (2,5,6). These overlapping mechanisms create a proarrhythmic substrate capable of producing ventricular tachycardia, ventricular fibrillation, and transient Brugada-like electrocardiographic patterns (2,5).
Cocaine’s multi-channel cardiac toxicity and catecholamine surge predispose to malignant arrhythmias, highlighting the importance of early recognition and supportive interventions.
Clinical manifestations of cocaine-induced sodium channel toxicity range from asymptomatic conduction delay to unstable wide-complex arrhythmias and sudden cardiac arrest. Electrocardiographic findings suggestive of sodium channel blockade include QRS duration exceeding 100–120 ms, a prominent terminal R wave in lead aVR, and rightward terminal QRS axis deviation (2,4). Progressive QRS widening with increasing heart rate is particularly concerning and correlates with arrhythmic risk (2,4).
Metabolic acidosis, electrolyte abnormalities, co-ingestion of other cardiotoxic substances, and underlying structural heart disease or channelopathies may exacerbate toxicity (2,6).
Management priorities include airway protection, seizure control, and attenuation of sympathetic overactivity, most commonly with benzodiazepines (2,4).When sodium channel blockade is suspected, intravenous sodium bicarbonate is the treatment of choice (2,4,6).
The therapeutic benefit of sodium bicarbonate is attributed to serum alkalinization, which reduces drug–channel binding affinity, and increased extracellular sodium concentration, which competitively mitigates channel blockade (2,4). These effects frequently result in rapid QRS narrowing and hemodynamic improvement. Repeated boluses or infusion may be required, guided by ECG response and acid–base status.
Antiarrhythmic agents with sodium channel–blocking properties should be avoided, and β-blockers lacking α-adrenergic antagonism should be used cautiously due to the risk of unopposed vasoconstriction (7). In refractory cases, lipid emulsion therapy or extracorporeal life support may be considered (2,6).
Conclusion
Cocaine-related cardiotoxicity is multifactorial, with direct, use-dependent sodium channel inhibition representing a central and potentially reversible mechanism. In patients presenting with wide QRS tachyarrhythmias and suspected stimulant exposure, toxic sodium channel blockade should be promptly considered. Early ECG recognition and timely administration of sodium bicarbonate, in conjunction with comprehensive supportive care, can be lifesaving.
Reference
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